It has been found desirable to limit the pressure within an inflating, deploying air bag to a predetermined maximum. Conventional means for limiting this pressure comprise the use of openings or vents in the air bag itself. In one such arrangement these vents are open during the entire air bag deployment. By venting the air bag to ambient atmosphere, the pressure within the air bag may be maintained at or below this predetermined level.
In another arrangement these vents are activated only upon the air bag pressure reaching a predetermined level. One such arrangement for limiting air bag pressure is disclosed in U.S. Pat. No. 4,989,895 - Pearson et al which utilizes force actuated venting of the air bag when air bag pressure reaches a predetermined maximum level. In this arrangement, air bag venting occurs when the reaction force on the inflator and its mounting support generated by the internal air bag pressure, resulting from engagement with the occupant of the air bag, exceeds the predetermined pressure level. The air bag support includes vents that are closed by rupturable diaphragms mounted above rupture pins. Collapsible columns mount the support and inflator and maintain the diaphragms above the pins. When a reaction force exceeds a predetermined level, the supports collapse, carrying the support and inflator with it so that the pins rupture the diaphragms to vent the air bag to ambient. With this arrangement, no venting will occur unless the predetermined pressure is reached. However, this improvement is gained through use of a physical arrangement requiring a plurality of collapsible columns, rupturable diaphragms and piercing pins. Also the process is a "one shot" action which is irreversible.
It would be desirable to provide a pressure limiting device for an air bag which is activated only upon air bag pressure reaching a predetermined level, but which is simple in concept and construction.